This article describes how to use a Ten Tec 1051 noise bridge kit as a
transmatch tuning accessory similar to the MFJ 212. The MFJ unit costs
about $100. The Ten Tec unit only costs $20 but requires construction of a
cabinet and switching to package it as a working system. The Ten Tec unit
consists only of a circuit board and components to build the bridge part of
UPDATE MARCH 2016: Ten Tec is going through some changes. The board and kit are still available for $21, but hard to find. Here is a link to the manufacturer's website and how to order:
The Ten Tec includes a slow keying unit which does not work well with
vintage receivers, which did not have very effective "hang" AGC. I changed
capacitor C3 from 1 uF to 0.1 uF to speed it up.
I also included a replacement high intensity large LED instead of LED 1 as
furnished by Ten Tec. This ensures that you will see it blinking and not
transmit into the noise bridge.
The Ten Tec includes a modulation scheme which does not work well with some
sharp corner modern filters. On the Ten Tec site, in the review section,
Glen Gardner suggests the following:
- Use a 14 pin DIP socket
- Bend pin 9 up and away from the socket so it does not plug in.
- Bridge pins 9 and 10 on the circuit board.
- Set R6 to mid range. Do not change it, regardless of Ten Tec setup instructions.
This makes it work better on SSB/CW with newer radios.
When paired with my change to C3, the Ten Tec 1051 works exactly like the
MFJ unit, and is perfect for off air adjustment of transmatches.
The switching circuitry that is required for integration into a station is
on page 14 of the Ten Tec manual. I recommend installation of the fuse as
shown. This is not as good as the protection relay and transmit sense
circuit of the MFJ unit. You could design a RF detect and switching circuit
to implement this as well. But the relay would add expense.
In my application, I have the Ten Tec 1051 in front of my HQ 180, but after
the T/R relay in my station, so it is impossible to transmit into the noise
bridge. So the extra expense of the RF sense and switch through relay is
The pictures show the construction into a Radio Shack metal enclosure (DO
NOT USE PLASTIC!). Be sure that the toggle switch reads ZERO OHMS. I found
a number of these in my junk box that were OK for switching AC power, but
had some resistance due to corrosion or poor choice of materials.